Deposition of copper by immersion



June 8, 1954 NQRWITZ 2,680,711

DEPOSITION OF COPPER BY IMMERSION Filed March 10 1950 ALUMINUM 0R ALUMINUM ALLOY 1. ECTR/CAL CONNECT/01V PM TING. SOLUTION AzuM/An/M 0R ALUMINUM ALLOY /]60/V TANK 1'2 Ec'TR/ (A 1. Comvscr/on/ INVENTOR GEORGE ORW/TZ Patented June 8, 1954 OFFICE DEPOSITION OF COPPER BY IMMERSION George Norwitz, Philadelphia, Pa.

Application March 10, 1950, Serial No. 149,034

The present invention relates to improvements in the immersion deposition of metals on unlike metal surfaces from aqueous solutions and provides means whereby a smooth, bright, dense, and strongly adhering deposit over an extensive surface may be obtained. More particularly, the invention relates to the immersion deposition of copper on aluminum and aluminum alloys and provides an advantageous process whereby this may be readily accomplished.

It has heretofore been proposed to deposit copper, for instance, on iron or low alloy steel simply by immersing the metal, i. e., the iron or steel, in an acid aqueous solution of copper sulfate. This procedure is known as immersion deposition. It is to this general type of process which the present invention relates and it is not to be confused with electroplating, electrorefining, or other electrodeposition in which an electric current from an extraneous source is passed through the solution.

Immersion deposition from an aqueous solution is inexpensive to operate and has many other desirable aspects, including the avoidance of the use of special electrodes and the handling of electric current. It has, however, been subject to serious limitations and diificulties. One difliculty heretofore experienced with this type of deposition has been the fact that the deposit formed is relatively readily rubbed or worn-off,

from the undersurface, particularly where relatively large objects are so plated. In addition to this lack of adequate adherence, the deposit is frequently dull, rough and uneven. This lack of adherence makes buffing or other polishing tedious, if not impossible. Further, the choice of metal bases on which the deposit could heretofore be formed by simple immersion deposition has been rather limited.

To my knowledge, no satisfactory method has heretofore been devised for depositing copper on aluminum or aluminum alloys without the aid of electric current.

I have found that adherent bright and dense deposits of copper may be formed on aluminum and on aluminum alloys from an aqueous bath by immersion deposition, if there is included in the bath a relatively large proportion Of a colloid, for instance, gelatin, agar agar, gum arabic, glue, casein, dextrose, dextrin, or the like and the aluminum or aluminum alloy piece on which the copper is to be plated be connected by means of an electrical conductor with the surface of a piece of iron also in contact with or immersed in the liquid bath. The use of gelatin 5 Claims. (Cl. 204-52) for this purpose has been found particularly advantageous.

It has previously been proposed in electrodeposition to include a colloid in the electrolyte bath. According to these proposals, only very small proportions of the colloid are used. In the electrodeposition of metals, the function of the colloid isgenerally understood to be in some way directly related to the passage of the electric current through the solution, for instance, to affect the current density, or to act as a movable diaphragm or to be carried by the electric current to the cathode and there neutralized.

It was not to be expected, therefore, that the addition of a colloid to the bath used in immersion deposition would advantageously influence the operation. As a'matter of fact, the use of colloids in such minor proportions as are permissible in electrodeposition baths, has been found ineffectual for applicants purpose.

Further, previous investigation of the use of such colloids in immersion deposition baths has failed to produce satisfactory results. It was found that the'inclusion of small proportions of colloids, i. e., less than 0.2%, in the immersion bath somewhat improved the immersion deposition of zinc, cadmium and tin on aluminum. However, the deposits so obtained were unsatisfactory and the procedure has been of little or no commercial importance.

The amount of colloid used, in accordance with my present invention, is of an entirely different order of magnitude. To be effectual, one should not use less'than about of the colloid on the total weight of the bath. The maximum proportion to be used is subject to some variation, but generally should not exceed about 1.5%. In general, I prefer to use gelatin as the colloid and in proportions within the range of 0.75% to 1.25%. An amount of colloid in excess of 1.5% is generally not desirable as its additional cost is not justified by proportionately improved results.

In accordance with the process of my present invention, the aluminum or aluminum alloy to be plated is immersed in a copper bath containing a colloid of the type and in the proportions just described, the aluminum or aluminum alloy piece being electrically connected to a piece of iron also immersed in the copper bath or in 'contact therewith. By this process, adherent,

bright and dense deposits of copper are obtained on the aluminum or aluminum alloy piece where without the iron no deposit of copper whatever is obtained on these materials.

The colloid, gelatin solution, for instance, is conveniently added to the bath at a temperature of 70 C., or higher, in order to obtain adequate fluidity and mixing. The object on which the deposit is to be formed is immersed in the result ant bath for to minutes and then removed and washed with water.

The electrical connection between the aluminum or aluminum alloy piece to be plated and the iron may be by actual contact with the iron 1 immersion deposition of my present invention may, with advantage, be effected.

Figure 1 of the drawings represents a vertical sectional view of an immersion tank in which a separate piece of iron is immersed in the copper bath and electrically connected with the piece of aluminum or aluminum alloy, and

Figure 2 represents a vertical section of an iron immersion tank in which the piece to be plated is electrically connected with the iron tank.

In Figure 1, the tank I may be constructed of iron, but may be of wood or other suitable material. The aluminum or aluminum alloy piece 2 to be plated is suspended in the copper bath 3 by hook 4 from rod 5, advantageously of wood, or other non-conducting material. The iron piece 6 is likewise suspended in the copper bath by hook I also supported by rod 5. The iron piece 6 is electrically connected with the piece 2 by means of an electrical connector 8, for instance, a piece or iron wire.

In Figure 2, the immersion tank i is constructed of iron, the piece 2 being electrically connected with the tank by means of conductor 8, thus avoiding the necessity of using a sep' or NJ -250 ml. of 10% copper sulfate solution 20-30 ml. of concentrated sulfuric acid 150-250 ml, of hot 5% gelatin solution.

It will be appreciated, of course, that, in place of copper sulfate, other copper salts may be used, for instance, copper chloride or copper nitrate.

Reference to aluminum alloys herein, and in the appended claims, is not to be interpreted to include metals or alloys containing only minute amounts, or insignificant quantities, of aluminum, but is to be understood to mean alloys in which aluminum is a principal ingredient.

I claim:

1. A process for the immersion deposition of copper on a metal from the group consisting of aluminum and aluminum alloys which comprises immersing the metal on which the copper is to be deposited in an acidic aqueous solution of a copper salt containing. a colloid of the group consisting of gelatin, agar agar, gum arabic, glue, casein, dextrose and dextrin in proportions within the range of /'2% to 1 /z% by weight of the solution, the metal on which the copper is to be deposited being electrically connected with a piece of iron, also in contact with the copper salt solution.

2. The process of claim 1 in which the proportion of the colloid included in the copper salt solution is equivalent to 158 to 250 milliliters of a 5% solution of the colloid per liter of the electrolyte solution.

3. The process of claim 2 in which the is gelatin.

4. The." process of claim 2 in which the colloid is glue.

5. The process of claim 2 in which the composition of the plating solution is within the following indicated range:

150-250 ml. of 10% copper sulfate solution 20450 ml. of concentrated sulfuric acid 150-250 ml. of hot 5% colloid solution.

colloid References Cited in the file of this patent UNITED STATES PATENTS 

1. A PROCESS FOR THE IMMERSION DEPOSITION OF COPPER ON A METAL FROM THE GROUP CONSISTING OF ALUMINUM AND ALUMINUM ALLOYS WHICH COMPRISES IMMERSING THE METAL ON WHICH THE COPPER IS TO BE DEPOSITED IN AN ACIDIC AQUEOUS SOLUTION OF A COPPER SALT CONTAINING A COLLOID OF THE GROUP CONSISTING OF GELATIN, AGAR AGAR, GUM ARABIC, GLUE, CASEIN, DEXTROSE AND DEXTRIN IN PROPORTIONS WITHIN THE RANGE OF 1/2% TO 1 1/2% BY WEIGHT OF THE SOLUTION, THE METHAL ON WHICH THE COPPER IS TO BE DEPOSITED BEING ELECTIRCALLY CONNECTED WITH A PIECE OF IRON, ALSO IN CONTACT WITH THE COPPER SALT SOLUTION. 